The life loss is based on the power of the sacrificed creature as it last existed on the battlefield.

10/1/2012

To activate Jarad’s last ability, you must sacrifice two lands. It doesn’t matter what other land types the two lands have, as long as one is a Swamp and one is a Forest. Even if one of the lands you sacrifice is both a Swamp and a Forest, you have to sacrifice another land that is a Swamp or a Forest.

10/1/2012

You can sacrifice any land with the land type Swamp or Forest, not just ones named Swamp or Forest. For example, you could sacrifice two Overgrown Tombs.